Method for anion-exchange adsorption and thioether anion-exchangers

Abstract

A method for the removal of a substance, which has a negative charge and which is present in an aqueous liquid (I). The method comprises the steps of: (i) contacting the liquid with an anion-exchanger (1) that comprises mixed mode anion-exchanging ligands in which there is a positively charged nitrogen allowing binding of the substance to the anion-exchanger; and (ii) desorbing said substance from said anion-exchanger. The characteristic feature is that (A) the mixed mode ligands have a thioether linkage within a distance of 1-7 atoms from their positively charged atom, and (B) the anion-exchanger (1) (i) is capable of binding the substance of interest in an aqueous reference liquid (II) at an ionic strength corresponding to 0.25 M NaCl, and (ii) permits in the pH interval 2-12 a maximal breakthrough capacity for the substance which is ≧200% of the breakthrough capacity of the substance for Q-Sepharose Fast Flow (anion-exchanger 2).

1. A method for the removal of a substance carrying a negative charge from an aqueous liquid (I), said method comprising the steps of
 i) contacting the liquid with an anion-exchanger (1) that comprises a base matrix carrying a plurality of mixed mode anion-exchanging ligands in which there is a positively charged nitrogen under conditions permitting binding between the ligands and the substance; and 
 ii) desorbing said substance from said anion-exchanger by the use of a liquid (liquid (II)), 
 wherein 
 (A) all or a part of the plurality of mixed mode anion-exchange ligands have a thioether linkage within a distance of 1-7 atoms from its positively charged nitrogen, and 
 (B) the anion-exchanger (1) is
 (a) capable of binding the substance of interest in an aqueous reference liquid (II) at an ionic strength corresponding to 0.25 M NaCl, and 
 (b) exhibits in the pH interval 2-12 a maximal breakthrough capacity for the substance of at least 200% of the breakthrough capacity of the substance for Q-Sepharose Fast Flow, 
 
 
       said anion-exchangers having essentially the same ligand density and breakthrough capacities being determined under the same conditions. 
     
     
       2. The method of  claim 1 , wherein each thioether-containing anion exchange ligands are of the formula:
   --SP---[R 5 —S—R 1 —N + (R 2 R 3 R 4 )]
 
 
       where:
 SP is a spacer that attaches the ligand [R 5 —S—R 1 —N + (R 2 R 3 R 4 )] to the base matrix, 
 --- represents that the spacer replaces a hydrogen in [R 5 —S—R 1 —N + (R 2 R 3 R 4 )], 
 -- represents a link to the base matrix, 
 R 1  is a bivalent group selected among linear, branched or cyclic hydrocarbon groups, and 
 R 2-5  are monovalent groups selected among the same kind of hydrocarbon groups as R 1  or divalent forms of these hydrocarbon groups, with the proviso that a carbon chain in R 2-5  possibly is interrupted at one or more positions by a thioether sulphur. 
 
     
     
       3. The method of  claim 1 , wherein at least one of the anion-exchange ligands and/or the anion-exchanger has a pKa ≦12. 
     
     
       4. The method of  claim 2 , wherein R 1  contains one or more of the following
 (a) an aromatic system, 
 (b) unsaturation, 
 (c) one or more atoms or groups participating electron donor-acceptor interactions, 
 (d) a carbon chain that is interrupted at one or more positions by ether oxygen, and/or amine nitrogen, at least one of said one or more atoms or groups participating in electron donor acceptor interactions being at a distance within the interval of 1-7 atoms from the positive nitrogen atom. 
 
     
     
       5. The method of  claim 2 , wherein at least one of said one or more atoms or groups participating electron-donor-acceptor interactions are present are present in a branch in SP or as a part of the chain of atoms in SP extending from the base matrix to the ligand. 
     
     
       6. The method of  claim 2 , wherein SP includes
 (a) a carbon atom with preference for a carbonyl carbon or an sp 3 -hybridised carbon; or 
 (b) a nitrogen atom with preference for an amino or amido nitrogen; or 
 (c) a sulphur atom with preference for a thioether sulphur atom; or 
 (d) an oxygen, with preference for an ether oxygen atom; 
 directly attached to the ligand [R 5 —S—R 1 —N + (R 2 R 3 R 4 )]; 
 with the proviso that SP always is attached to a carbon in R 1  for (b)-(d). 
 
     
     
       7. The method of  claim 1 , wherein the ionic strength during the adsorption/binding step (i) is larger or equal with the ionic strength of 0.25 M NaCl water solution. 
     
     
       8. The method of  claim 1 , wherein the pH of aqueous liquid (I) is ≦pKa+2 of the anion-exchanger or of ligands [R 5 —S—R 1 —N + (R 2 R 3 R 4 )]. 
     
     
       9. The method of  claim 1 , wherein the pH of the aqueous liquid (II) is different from the pH of aqueous liquid (I) in order to decrease the negative charge of the substance. 
     
     
       10. The method of  claim 1 , wherein the polarity of the aqueous liquid (II) is lower than the polarity of aqueous liquid (I). 
     
     
       11. The method of  claim 1 , wherein the aqueous liquid (II) includes a structural analogue of the ligand in a larger concentration than in the aqueous liquid (I). 
     
     
       12. The method of  claim 4 , wherein
 (i) said electron donor-acceptor interaction is hydrogen bonding and/or 
 (ii) donor atoms/groups are selected among:
 (a) oxygen with a free pair of electrons, such as in hydroxy, ethers, carbonyls, and esters (—O— and —CO—O—) and amides, 
 (b) sulphur with a free electron pair, such as in thioether (—S—), 
 (c) nitrogen with a free pair of electron, such as in amines, amides including sulphone amides, 
 (d) halogen (fluorine, chlorine, bromine and iodine), and 
 (e) sp- and sp 2 -hybridised carbons; and/or 
 
 (iii) acceptor groups are selected amongst groups that consists of a electron-deficient atom, such as hydrogen, and/or an electronegative atom. 
 
     
     
       13. The method of  claim 3 , wherein the anion-exchange ligands containing thioether linkages are primary or secondary amines. 
     
     
       14. An anion-exchanger (1) comprising a plurality of anion-exchange ligands each of which is attached via a spacer to a hydrophilic base matrix, wherein
 (a) each ligand plus spacer has the formula:
   --SP---[R 5 —S—R 1 —N + (R 2 R 3 R 4 )]
 
 wherein 
 (i) SP is a spacer that attaches the ligand [R 5 —S—R 1 —N + (R 2 R 3 R 4 )] to the base matrix, 
 (ii) --- represents that the spacer replaces a hydrogen in [R 5 —S—R 1 —N + (R 2 R 3 R 4 )], 
 (iii) -- represents a link to the base matrix, 
 (iv) R 1  is a bivalent group selected among linear, branched or cyclic hydrocarbon groups, and 
 (v) R 2-5  are monovalent groups selected among the same kind of hydrocarbon groups as R 1  or divalent forms of these hydrocarbon groups, with the proviso that a carbon chain in R 2-5  possibly is interrupted at one or more positions by a thioether sulphur; 
 
 (b) the anion-exchanger (1) has a maximal breakthrough capacity in the pH-interval 2-12 for at least one reference protein selected amongst ovalbumin, conalbumin, bovine serum albumin, β-lactoglobulin, α-lactalbumin, lysozyme, IgG, soybean trypsin inhibitor (STI) which is at least 200% of the maximal breakthrough capacity in the pH-interval 2-12 obtained for a Q-exchanger (—CH 2 CH(OH)CH 2 N + (CH 3 ) 3 ) (anion-exchanger  2 ), the support matrix, degree of substitution, counter-ion and running conditions being the same for anion-exchanger (1) and anion-exchanger (2). 
 
     
     
       15. The anion-exchange of  claim 14 , wherein the relative breakthrough capacity is measured under anion exchange conditions. 
     
     
       16. The anion exchanger of  claim 14 , wherein R 1  contains one or more of the following
 (a) an aromatic system, 
 (b) unsaturation, 
 (c) one or more atoms or groups participating electron donor-acceptor interactions, 
 (d) a carbon chain that is interrupted at one or more positions by ether oxygen, and/or amine nitrogen, at least one of said one or more atoms or groups participating in electron donor acceptor interactions being at a distance within the interval of 1-7 atoms from the positive nitrogen atom.